The present invention generally relates to a raised floor system used in a semiconductor fabrication facility and more particularly, relates to a raised floor system that is formed of octagonal panels mounted to square-topped pedestals that is capable of sustaining large deformation without collapsing.
In the recent development of semiconductor fabrication technology, the continuous miniaturization in device fabricated demands more stringent requirements in the fabrication environment and contamination control. When the feature size was in the 2 xcexcm range, a cleanliness class of 100xcx9c1000 (i.e., the number of particles at sizes larger than 0.5 xcexcm per cubic foot) was sufficient. However, when the feature size is reduced to 0.25 xcexcm, a cleanliness class of 0.1 is required. It has been recognized that an inert mini-environment may be the solution to future fabrication technologies when the device size is reduced further. In order to eliminate micro-contamination and to reduce native oxide growth on silicon surfaces, the wafer processing and the loading/unloading procedures of a process tool must be enclosed in an extremely high cleanliness mini-environment that is constantly flushed with ultra-pure nitrogen that contains no oxygen and moisture.
Different approaches in modern clean room design have been pursued in recent years with the advent of the ULSI technology. One is the utilization of a tunnel concept in which a corridor separates the process area from the service area in order to achieve a higher level of air cleanliness. Under the concept, the majority of equipment maintenance functions are conducted in low-classified service areas, while the wafers are handled and processed in more costly high-classified process tunnels. For instance, in a process for 16M and 64M DRAM products, the requirement of contamination control in a process environment is so stringent that the control of the enclosure of the process environment for each process tool must be considered. This stringent requirement creates a new minienvironment concept which is shown in FIG. 1. Within the enclosure of the minienvironment of a process tool 10, an extremely high cleanliness class of 0.1 (i.e., the number of particles at sizes larger than 0.1 xcexcm per cubic foot) is maintained, in contrast to a cleanliness class of 1000 for the overall production clean room area 12. In order to maintain the high cleanliness class inside the process tool 10, the loading and unloading sections 14 of the process tool must be handled automatically by an input/output device such as a SMIF (standard mechanical interfaces) apparatus.
FIG. 1 also shows a raised floor system 30. The raised floor system 30 is normally installed between 45 and 60 cm above the finished concrete waffle slab 32. The raised floor system 30 generally, covers the entire clean room production area. The grid 34 of the raised floor is based on a 60xc3x9760 cm system and is normally aligned with the center lines of the filter ceiling grid. Some of the floor tiles 36 are perforated for circulating the clean room air 38. The adjustment of the air pressure in the clean room and the balancing of air flow can be achieved by selecting floor tiles with proper perforations.
In the raised floor system 30 shown in FIG. 1, the floor tiles 36 should be static-dissipative and made of non-combustible material that is also chemical abrasion resistance. A frequently used material is vinyl which is impact resistant and meets the electrostatic discharge isolation resistance requirement for the clean room environment.
A detailed, cross-sectional view of a raised floor system 30 is shown in FIG. 2. The raised floor system 30 should be laterally stable in all directions with or without the presence of the floor tiles 36. This is achieved by anchoring the pedestals 40 into the concrete slab floor 32 and by the further use of stringers 42 and steel braces 44. The floor tiles are supported by the stringers 42 which are in turn supported at each corner by adjustable height pedestals 40. As shown in FIG. 2, the pedestals 40 are bolted to the finished concrete waffle slab 32. An insulation plate 46 placed on top of each pedestal 40 attenuates foot-step sound and ensures electrical isolation. The steel braces 44 are used to further increase the rigidity of the raised floor system 30 and the pedestal support.
In recent years, for safety considerations such as for minimizing the risk from earthquake vibration in a highly stacked fab plant, screws or bolts are required at each corner of the raised floor panels 36. However, even with the screw attachments, a raised floor system 30 with square panels cannot be deformed to a large extent without collapsing or failure.
In a raised floor system that is formed of square or rectangular panels, as that shown in FIGS. 3 and 5, a force acting on one panel can only be transferred to one immediate adjacent panel (See FIG. 5) or through the boundaries between the panels to a support or a pedestal (See FIG. 3B). The result of a stress analysis for a conventional raised floor system utilizing rectangular panels is shown in FIG. 3. The data obtained for each panel is calculated by the equation of: Sigma=Fs+m=0.25 F+L * 0.25 F. The stresses calculated are significantly higher than a raised floor system equipped with octagonal panels shown in FIG. 4C.
In the conventional raised floor system equipped with square or rectangular panels, the force acting on one panel during an earthquake cannot be transmitted to all directions, instead only to one direction as shown in FIGS. 3B and 5. The large force, or stress transmitted to the next panel leads to possible cracking in the panel or in pedestal support system which may lead to a dislocation of process machines situated on the raised floor. The dislocation of the process machines may in turn cause breakage of conduits that feed corrosive or poisonous chemicals to the process machines and serious leakage and contamination problems in the fab facility.
It is therefore an object of the present invention to provide a raised floor system for a semiconductor clean room facility that does not have the drawbacks or shortcomings of conventional raised floor systems.
It is another object of the present invention to provide a raised floor system for a semiconductor clean room facility constructed of octagonal-shaped panels.
It is a further object of the present invention to provide a raised floor system for semiconductor clean room facility constructed of octagonal panels mounted on pedestals that have square top surfaces forming part of the floor.
It is still another object of the present invention to provide a raised floor system for semiconductor clean room facility equipped with octagonal panels having a raised peripheral ridge on a bottom side for mounting to recessed peripheral slots on pedestals.
It is still another object of the present invention to provide a raised floor system for semiconductor clean room facility that is constructed of octagonal panels each has a flat top surface and a convex bottom surface equipped with a raised peripheral ridge for engaging onto four pedestals.
It is yet another object of the present invention to provide a raised floor system for semiconductor clean room facility that is constructed of octagonal panels wherein a plurality of pedestals each has a top portion and a base portion threadingly engaged together for adjusting a height of the pedestal is used.
In accordance with the present invention, a raised floor system for use in a semiconductor clean room facility that is formed of octagonal-shaped panels and square-topped pedestals is provided.
In a preferred embodiment, a raised floor system constructed of octagonal panels is provided which includes a plurality of pedestals each has a top portion and a base portion threadingly engaged together for adjusting a height of the pedestal, the top portion has a square top surface and four recessed peripheral slots surrounding the top surface, each of the four recessed peripheral slots is adapted for engaging an octagonal panel, and a plurality of octagonal panels each has a flat topped surface and a convex bottom surface equipped with a raised peripheral ridge for engaging one of the recessed slots on the top portion of the pedestal such that the flat top surface of the octagonal panel is coplanar with the square top surface of the pedestal when the panel is assembled to the pedestal.
In the raised floor system constructed of octagonal panels, the octagonal panels each has an octagonal shape of equal sides. The top portion and the base portion of the pedestal threadingly engages each other by a screw shaft stationarily mounted in the base portion. The raised floor system may further include at least one height-adjusting collar that has female threads therein for engaging the screw shaft for supporting the top portion of the pedestal and for turning on the screw shaft for raising or lowering the top portion of the pedestal. The raised floor system may further include a locking collar that has female threads therein for engaging the screw shaft, the locking collar may be positioned on top and for locking a position for the at least one height-adjusting collar such that a height of the pedestal is locked.
In the raised floor system, the convex bottom surface of the plurality of octagonal panels may further include a plurality of rib sections for reinforcing a rigidity of the panels. The convex bottom surface of the plurality of octagonal panels may further include a plurality of rib sections arranged peripherally around a center of the panel, the rib sections may have a height of at least 0.5 cm. The plurality of pedestals and the plurality of octagonal panels may be fabricated of a high rigidity metal, such as aluminum or steel. The at least one height-adjusting collar may have a knurled section on an outer surface to facilitate gripping by human hand. The four recessed peripheral slots surrounding the top surface of the top portion of the pedestal each may have a depth of at least 2 cm for receiving the raised peripheral ridge of the octagonal panels. The raised peripheral ridge of the octagonal panels may have a height of at least 1 cm. A largest linear dimension on the octagonal panels is about 60 cm, a thickness of the octagonal panels is about 1 cm. The plurality of pedestals and the plurality of octagonal panels may be fabricated of aluminum.